Mexican Hat PEA Plans a 10,000 t/d Contractor-Crushed Heap Leach With a Two-Train Carbon-in-Column ADR Plant

GMV Minerals' August 2025 updated preliminary economic assessment for the Mexican Hat gold project in Cochise County, Arizona, crushes 3.5 Mt a year to 38 mm and stacks it in 10 m lifts on a 32.6 Mt pad.

The NI 43-101 Technical Report, Updated 2025 Preliminary Economic Assessment, Mexican Hat Project, Cochise County, Arizona, was prepared for GMV Minerals Inc. with an effective date of August 8, 2025 and an issue date of August 20, 2025. The deposit is to be mined by open pit. A contractor will run a two-stage crushing plant at a nominal 10,000 t/d. The crushed ore will be heap leached with cyanide, and gold will be recovered in an adsorption, desorption and recovery (ADR) plant supplied as a vendor package.

Critical Data

Overview

Run-of-mine ore is crushed in two stages from 1,400 mm to 80% passing 38 mm and conveyed to a stockpile with 24 hours of live capacity. Two 4 by 15 ft feeders reclaim it onto a 1,000 m long, 42 inch overland conveyor, with lime added on the way. Grasshopper conveyors and a radial stacker place it on the heap leach pad. Cyanide solution is applied, and the pregnant leach solution (PLS) is collected in a lined pond and pumped to the ADR plant.

Key Process Stages

Crushing. The two-stage plant is supplied, operated and maintained by the crushing contractor. It is designed to crush 3.5 Mt a year at 75% availability.

Stacking and leaching. Ore is stacked 12 hours a day at 833 t/h in 10 m lifts. The heap leach facility (HLF) is built in two phases, of about 192,201 m² and 373,311 m², for a total capacity of 32.6 Mt at a heap density of 1.5 t/m³. Phase 1 holds about two years of ore in four lifts. Phase 2 expands west to hold the life-of-mine ore in seven lifts, to a maximum heap height of 72 m at an overall slope of 2.5H:1V.

Carbon adsorption. PLS is pumped through two trains of five carbon-in-column (CIC) tanks in series, with carbon advanced counter-current so the richest solution meets the most loaded carbon. Loaded carbon is transferred daily to elution.

Acid wash and elution. Carbon is acid washed with hydrochloric acid at atmospheric pressure, rinsed for 30 minutes, and stripped under pressure at about 145°C with caustic strip solution. About 11 bed volumes are pumped at 2 bed volumes an hour through the electrowinning cells.

Electrowinning and refining. Two electrowinning cells plate gold onto steel wool. A 20% bleed of barren solution is recommended to prevent contaminant build-up. Sludge is filter pressed, oven dried, retorted for mercury and smelted in an electric induction furnace at about 1,230°C to doré.

Carbon regeneration. Stripped carbon is regenerated in a horizontal rotary kiln at 750°C after every strip. The report notes that skipping regeneration lowers loading efficiency and increases gold losses in solution.

Additional Interesting Data and Summary

The HLF liner is a composite of 80-mil double-sided textured LLDPE geomembrane over a geosynthetic clay liner or low-permeability soil (no more than 1×10⁻⁶ cm/s), on compacted bedding. It is protected by at least 0.6 m of free-draining overliner, with a herringbone network of 100 mm perforated pipes at up to 6 m centres feeding 450 mm and 600 mm collectors. Two ponds serve the pad: a PLS pond and an event pond sized for the 100-year, 24-hour storm. The design is to meet or exceed the Arizona Department of Environmental Quality's prescriptive BADCT criteria.

In summary, the 2025 Mexican Hat PEA is a conventional Arizona crushed-ore heap leach at 10,000 t/d, with contractor crushing to 38 mm, a tall two-phase pad and a packaged two-train CIC ADR plant.

Key Processes

• Contractor two-stage crushing to 80% passing 38 mm
• Stockpile reclaim and overland conveying with lime addition
• Grasshopper and radial stacker placement in 10 m lifts
• Cyanide heap leaching on a composite-lined pad
• Two-train carbon-in-column adsorption
• Acid wash and pressure elution
• Electrowinning, mercury retorting and induction smelting
• Rotary kiln carbon regeneration

Source: NI 43-101 Technical Report, Updated 2025 Preliminary Economic Assessment, Mexican Hat Project, Cochise County, Arizona, USA, prepared for GMV Minerals Inc., effective date August 8, 2025.